1. Field of the Invention
The present invention relates to a shutter control method for a multi-sputtering system. It also relates to a double-layer shutter control method suitable for preventing cross-contamination in a multi-sputtering system providing a plurality of targets made of different materials in a single chamber and forming a multi-layer film utilizing a double-layer rotating shutter mechanism.
2. Description of the Related Art
The assignee previously proposed a magnetic multi-layer film-forming system (U.S. Patent Application Publication No. 2002/0064595). When producing a giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) head, MRAM, etc., this magnetic multi-layer film-forming system can form a required multi-layer film in a single chamber by sputtering from the lowermost layer to the uppermost layer on a substrate continuously without interruption and can deposit a large number of magnetic films at one time.
In order to enable formation of a multi-layer film by sputtering as described above, this film-forming system provides, for example, five targets made of different materials at a chamber ceiling, that is, the space above the substrate to be formed with the film, in a single chamber, then using a shutter mechanism for selecting the target for sputtering. This shutter mechanism has a double-layer structure of independently rotating shutters. Each of the two shutter plates is formed at required positions with a required number of holes through which selected targets can be seen from the substrate side. The double-layer rotating shutter mechanism shields the targets of the materials not being used for sputtering. The target for sputtering appears to the substrate through the corresponding holes. This double-layer rotating shutter mechanism independently rotates two substantially circular shutter plates as seen from a parallel arranged substrate. Due to this, matching positions of the holes of the shutter plates are selected. The double-layer rotating shutter mechanism is used so as to make the target made of the material being used for sputtering face the substrate through the holes so as to select the target for sputtering.
The above multi-layer film-forming system is a multi-sputtering system providing a plurality of targets made of different materials in a single sputtering chamber, sequentially depositing films made of different materials on a substrate, and thereby forming a multi-layer film. This multi-sputtering system, as explained above, suitably shields the five targets made of the different materials by the double-layer rotating shutter mechanism in the single sputtering chamber to select the target used for sputtering and thereby performs the sputtering according to a previously set film-forming sequence.
When selecting a plurality of targets made of different materials by the double-layer rotating shutter mechanism and using the same for sputtering in a specific sequence, cross-contamination may be caused between targets.
For example, sputtering includes a state of “pre-sputtering” causing a discharge to start the sputter state in the state with the target for sputtering covered by the shutter mechanism and a state of “main sputtering” completely opening the shutter mechanism to perform the sputtering on the substrate. At this time, cross-contamination will occur due to (1) deposition of different types of substances deposited on the surface of the shutter plate facing the target onto the target surface due to the sputtering action at the time of the pre-sputtering; (2) sputtering of different types of substances deposited on the target surface onto the substrate at the time of the main sputtering; (3) deposition of sputter atoms rebounding from the substrate in the middle of the main sputtering onto another target surface; and so on. When shifting from pre-sputtering to main sputtering by rotating the shutters for the pre-sputtering to shift to the main sputtering, the contamination explained in (1) occurs after locations where different types of substances are deposited are passed through during the rotation of the shutter plates. This becomes a conspicuous problem.
In order to deposit a multi-layer film with good film properties on a substrate, prevention of the various cross-contaminations described above becomes indispensable.
U.S. Patent Application Publication No. 2002/0064595 shows one method of operation in the double-layer rotating shutter mechanism in FIG. 5A and FIG. 5B thereof. This comprises positioning a target side first shutter plate and a substrate side second shutter plate in the initial state so as to position a hole of the second shutter plate with the target for sputtering and to position the holes of the first shutter plate away from the target for sputtering, then starting the pre-sputtering. This pre-sputtering is sputtering for removing oxides and other surface contaminants on the surface of the target. Next, the first shutter plate is rotated to align a hole thereof with the above hole of the second shutter plate to expose the target for sputtering with respect to the substrate and perform the main sputtering on the substrate. The main sputtering is the basic sputtering for the film formation. In this way, this shows an operation of the double-layer rotating shutter mechanism in the main sputtering for exposing only the target for sputtering with respect to the substrate at the time of the main sputtering to prevent the intermixture of the materials of the other targets and thereby prevent cross-contamination.
As explained above, however, cross-contamination is a complex phenomenon changing in accordance with the number of targets, the number of holes, and other conditions. Various types of cross-contamination occur. Further, the method of rotation of the shutter plates of U.S. Patent Publication No. 2002/0064595 does not discuss at all how to deal with the target materials deposited on the shutter plates at the time of the pre-sputtering. As described above, the method of operation of the double-layer rotating shutter mechanism disclosed in U.S. Patent Application Publication No. 2002/0064595 is not sufficient to deal with any cross-contamination which may occur.
Therefore, it is desired to provide a multi-sputtering system, provided with a plurality of targets made of different materials in a single sputtering chamber for sputtering of a multi-layer film on a substrate and provided with a double-layer rotating shutter mechanism for selecting a target for sputtering at the film formation space side of the plurality of targets, which prevents contamination of the other targets by the target substances deposited on the double-layer shutters along with the sputtering sequence of the multi-layer film by optimally controlling the sequence of the shield operation of the double-layer shutter plates.